So, 800 retweets and nearly 1000 favourites later, we thought you might like to know a bit more aboutaphercotropism, and thereby address a few of these queries (and the dozens more like them). Scalpels at the ready, then—let’s dissect this thing.

First of all,the prefixap–oraph–derives from a Greek word,apo, meaning “off” or “away from”. It’s the same root we see in words likeapocalypse(whichliterally means“uncovered” or “disclosed”),apocryphal (literally “hidden away”), and evenapology,which originally referred toa formal defence or justification, or to a personal account of a story (and so literally means “from speech”).

Secondly, the –erco– part comes from another Greek word,herkos, referring to a fence, a barrier, or a some kind surrounding wall. It only has a handful of offspring in modern English, the majority of which are fairly obscure, long-forgotten terms (the kind thatHaggardHawksdevours) that have found their way into the dustier corners of the OED:hercotectonic(“pertaining to the construction of walls”),poliorcetic(“relating to the besieging of cities”), andhercogamous, a botanical term describing plants that grow “barriers” between their male and female parts in order to prevent self-fertilization. Apparently.

So that only leaves the suffix–tropism, which you’ll likely recognise from words likeheliotropism(“turning towards the sun”) and phototropism (“growthtowards a light source”). Scientists and ecologists have inventeddozens of wordsfor different kinds of “tropism” besides these, of course, includinggeotropism(“growth dictated by gravity”), thigmotropism (“movement in response to touch”),homolotropism(“fixed horizontal growth”), and andthixotropism, which refers to the property of certain fluids that makes them act like a solid when subjected to a force—which is why you canrun across a pool of custard.

Wait a second—let me just stop to add those last six words to my bucket list… Right, let’s carry on.

Tropismderives fromanother Greek root,tropos, which literally means “a turning”. So when we put everything back together,aphercotropismultimately refers to an organism quite literally “turning away from an obstruction”. That’s all well and good, of course, but it still doesn’t explain where the word itself comes from. Did we just make it up?

Aphercotropism … is a peculiarity discovered by Darwin. His experiment was as follows: after allowing a radicle to be well developed in peas, beans, &c. the seed is suspended in the air. A tiny piece of card is attached to one side of the tip by a little gum; the tip will now move away from the vertical position, on the opposite side to the card. The tip may make one or more complete circles in a vertical plane; and it has been known to pass through the first loop so as to tie itself into a knot. This explains how a radish was once dug up and found to be thus tied up.

Charles Darwinoutlined this experiment—in which the root of a single pea plantgrows in an obscure shapein order to avoid the card glued above it—in his 1880 work,The Power of Movement in Plants. But in his account, he makes no reference to the wordaphercotropism. So until any other evidence comes to light, we can presume that the word was coined sometime between the publication of Darwin’s book in 1880, and the publication of theNature Notesjournal in 1899, the author of which likewise makes no reference to having coined the word himself. Precisely who did coin the word, ultimately, remains a mystery.

Right. Now, back to that custard thing…

____________________With grateful thanks to avid HH-er John (no surname supplied, unfortunately!) who emailed to say, quite rightly, that the second Greek root of aphercotropism discussed above should read herkos, not erkos as it did previously. For those of you not up to speed with your Ancient Greek (a minority, surely...) this is to do with “rough breathing”, an Ancient Greek diacritic marker that indicated the vowel in question was preceded by a “h” sound, which should be transliterated into English as an H, and which we had omitted the post has now been updated accordingly. Apologies for the oversight—a more up to date Dictionary of Ancient Greek has been purchased here at HaggardHawks HQ. The other has been unceremoniously banished to the back of the cupboard.